1. Field of the Invention
The invention relates generally to a power meter and, in particular, the invention relates to a high-frequency power meter with a large dynamic range.
2. Related Technology
Traditionally, diode power meters are used among others for measuring the power of high-frequency signals. A test signal is supplied to a detector diode. Because of the quadratic characteristic of the detector diode, an analog output voltage of the detector diode proportional to the power of the signal can be obtained.
However, with the use of a single detector, a small dynamic range of the power meter is obtained, because this operates only within the square law region of the detector diode. If the square law region is fully exploited, a reduction in the accuracy of measurement is additionally obtained at the limit of the square law region.
In response to this problem, DE 10 2007 047 009 A1 discloses a power meter with several measurement paths, which are designed for different power ranges of the test signal. In this context, the test signal is switched between the different measurement paths by a first switch at the input end. At the same time, exactly one measurement path is always active. Digitization of the test results is implemented after the combination of the measurement paths by means of an output-end, second switch. However, this power meter is associated with some disadvantages. For instance, signals with a rapid alternation between power ranges cannot be measured in a satisfactory manner, because the switches provide a switching latency. The properties of mechanical switches (for example, micro-mechanical MEMS switches) can vary subject to environmental influences and ageing. In particular, the contact resistance can increase. This results in a reduced accuracy of measurement.